New paper out in Cell reports on how our Heart Rate (HR) synchronize between people when we listen to engaging auditory narratives and watch videos. This work started as I pushed for not only measuring EEG as our subjects watched short educational videos, but also did eye tracking, ECG amongst other modalities. The first idea was simply that if people are more aroused i.e. higher HR then we would expect people to be more alert and pay more attention. However that didn’t actually turn out to be the case. Another frequently used measure is the Heart Rate Variability (HRV) which is also known to be an indicator of alertness, but we didn’t actually see that these measure could reliably predict attentional state nor how much people remember from narratives. Instead using the measure we also used for eye movements and pupil size, namely Intersubect Correlation of Heart rate turned out to be a robust measure of whether people were paying attention and how much they remember from the narratives that we played for people.